Modern integrated circuits are typically made of literally millions of active devices, such as transistors and capacitors. These devices are initially isolated from each other, but are later interconnected together to form functional circuits. Typical interconnect structures include lateral interconnections, such as metal lines (wirings), and vertical interconnections, such as vias and contacts. Interconnections are increasingly determining the limits of performance and the density of modern integrated circuits. On top of the interconnect structures, bond pads are formed and exposed on the surface of the respective chip. Electrical connections are made through bond pads to connect the chip to a package substrate or another die. Bond pads could be used for wire bonding or flip-chip bonding.
Flip-chip packaging utilizes bumps to establish electrical contact between a chip's input/output (I/O) pads and the substrate or lead frame of the package. Structurally, a bump actually contains the bump itself and an under bump metallurgy (UBM) layer located between the bump and an input/output (I/O) pad.
The orientation of a flip-chip package is often specified by markings on the package surface. The markings are placed on the package surface at the end of the packaging process. Determining the chip (or die) orientation prior to placing the markings is a challenge.